Common soil textures in Yolo County. Symbol size denotes relative abundance. The orange symbol represents a weighted average for the entire county.

Davis soils vary from moderately sandy (Reiff Series) in south and East Davis, through loamy soils (Yolo Series) in Central Davis, to heavy clay soils (Caypay Series) in west and North Davis. The spatial variation of soil properties in Davis is directly related to the fluvial deposition histories of the nearby streams. The heavy soils are found where low velocity waters of Putah Creek deposited material from the Coast Range. This material is notorious for having high concentrations of exotic elements; however the local high concentration of the element Boron is most likely from ground water. Sandier soils are found in locations where depositional energies were higher, or where material from the Sierra Nevada was incorporated. For specifics on the type of soil at your address, check out the UC Davis Soil Resource Lab's Online Soil Survey.

Use as a growth media

The soils found in and around Davis are often thought of as a poor growth medium. While this may be true for an uncultivated parcel of land where one attempts to plant seedlings by hand, but in terms of water storage capacity and nutrient storage the soils found here are some of the most productive in the world. The surface cracking observed in the summer is a result of the high content of smectiticclays, derived from weathered Coast Range rocks. The shrinking and swelling effects of these heavy clay soils (Capay Series) not only make it difficult to plant a vegetable garden, but also wreak havoc on houses or permanent structures. By incorporating copious amounts of mulch it is possible to create a rooting environment hospitable for seedlings, while retaining the high water holding capacity and nutrient store that the local soils offer. Similarly, you can lower the rate at which house plants dry out by incorporating a small amount of local soil into existing potting mix.

pH issues

The pH of soils found in and around the city of Davis range from neutral (7) to alkaline (> 8.5). While this condition does not affect plants native to this region, many plants may not be able to readily access several key micronutrients at this pH. As a general rule of thumb, a pH near 8.2 suggests that CaCO3 is the main buffering agent, and at pH near 8.5 Na2CO3 is the main buffering agent. It is very common in this region for soils with a high pH to also have a high sodium content as well. The sodium is usually more toxic than the high pH, although at higher pH values important micro nutrients such as Iron are less available to plants.

If you were to draw a rectangle around all of Davis and surrounding sprawl you would find that on a per-area basis only about 16% of the land has a moderately alkaline pH value (Yolo County Soil Survey).